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The postsynaptic density (PSD) is a cytoskeletal specialization at neuronal synapses that was originally identified as an electron-dense region at the membrane of a postsynaptic neuron, as viewed by electron microscopy. PSDs are usually comprised of L-glutamate neurotransmitter receptors, their molecular scaffolding molecules, cell adhesion molecules and a diverse set of other signaling proteins. PSDs vary in size and composition among brain regions. Many of the PSD proteins contain PDZ domains.
The PSD has been proposed to concentrate and organize neurotransmitter receptors to respond rapidly to neurotransmitter in the synaptic cleft. Some of the features of the PSD are similar to the neuromuscular junction and other cellular junctions, as the PSD has been modeled as a specialized cellular junction that allows for rapid, asymmetical signaling.
The structure and composition of the PSD have been the focus of numerous molecular studies of synaptic plasticity, a cellular model of learning and memory. PSDs are sized on the order of 0.25 to 0.5 micrometres in diameter and 0.025 to 0.05 micrometres in thickness, depending on the activity state of the synapse.
Many proteins in the PSD are involved in the regulation of synaptic function. Key among these, are postsynaptic density-95 (PSD95), neuroligin (a cellular adhesion molecule) NMDA receptors, AMPA receptors, calcium/calmodulin-dependent protein kinase II and actin. As protein detection technologies have increased in sensitivity, such as with improvements in mass spectroscopy techniques, more numerous proteins have been attributed to the PSD. Current estimates are greater than several hundred proteins are found at PSDs among brain regions and during different states of development and synaptic activity.
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Structure and CompostionEdit
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